Method of heat treating aluminum bronze alloy and product thereof



United States Patent i 2,870,051 Mnrnjon or HEAT TREATING ALUMINUMBRONZE ALLOY AND PRODUCT THEREOF John F. Klement, Milwaukee, Wis.,assignor to Arnpco Metal, Inc., Milwaukee, WiSL, a corporation ofWisconsln No Drawing. Application February 21, 1957 Serial No, 641,457

5 Claims. c1. us -21.92)

This invention relates to an aluminum bronze alloy having an increasedmodulus of elasticity and to a method of producing the same. Thisapplication is a continuation-in-part of the application, Serial No.371,192, filed.

Ju-ly 29, 1953, entitled Aluminum Bronze Alloy Struc ture and MethodofMaking the Same of the same inventor, now abandoned.

It is an accepted engineering fact that the modulus of elasticity of amaterial cannot ordinarily be changed any appreciable amount by heattreatment. However, the present invention is based on the discovery thatcertain metallographic phases of aluminum bronze, namely the duplex(alpha and beta) structure or the beta structure, can be heat treated ina manner to alter the modulus of elasticity. For certain specificapplications of aluminum bronze, such as shafting, bushings or machinemembers where an increase of rigidity is desirable,- the heat treat-.ment of the present invention can be most effectively used tosubstantially increase the modulus of elasticity.

An object of the invention is to provide an aluminum bronze alloy havinga substantiallyincreased modulus of elasticity over the normallyaccepted value and which is particularly adaptable for use as shafting,rolls or bush-v ings requiring high rigidity. I

Another object is to provide a method of increasing the modulus ofelasticity of an aluminum bronze alloy ,while also improving the otherphysical properties such as hard ness, yield strength and modulus ofrigidity. 7

Another object is to provide a heat treatment for a duplex phasealuminum bronze alloy whichserves to substantially increase the modulusof elasticity of the alloy while retaining .3 sufficient ductility forstructural design.

Other objects and advantages will appear in the course of the followingdescriptionz' i T o carry out the present invention the aluminum bronzealloy to be heat treated should have a certain metallographic structure,namely a duplex structure, consisting of alpha and beta phases, or abeta structure. I I

The me allog aphi st u of a p ticul r alum nu bronze is apt to varydepending on the alloying elements included therein. The ordinaryaluminum bronze composed of aluminum and copper and substantially freeof other alloying elements, will require above 9.5% aluminum in order topossess the preferred alpha and beta metallographic structure. Analuminum content in an ordinary aluminum bronze of below 9.5% willgenerally result in the alpha phase alone which will not bring about thedesired change in modulus of elasticity when sub jected to thepresentheat treatment. I 7

An aluminum content of over 12% in the ordinary 2 aluminum bronze willresult in the beta phase, which, as in the case of the duplex structure,is preferred. The aluminum concentration may be as high as- 20% in thenormal practice.

When the chemicalcomposition ofthe aluminum bronze is altered by theaddition of alloying elements, the proportion of aluminum required toobtain the duplex or beta structure may correspondingly vary. Forexample, it a metal having an aluminum absorbing power, such as iron,nickel, manganese or cobalt, is employed in the alloy, it may then benecessary to add as much as 16% by weight of aluminum to get thepreferred alpha and beta structure. With the small amounts of thesealloying additions normally employed, the necessary aluminum content maybe in the neighborhood of about 10.5% by weight of the alloy.

A typical illustration of an alloy composition containing aluminumabsorbing power ingredients and possessing a duplex structure is asfollows:

Percentage by weight Aluminum t 10.5 Iron 7 3.5 Copper Balance Incontrast to this composition, a lower aluminum content may be employedin order to obtain the duplex or beta structure when tin or silicon arepresent in the alloy. These materials tend to increase the formation ofthe beta constituent, and act very much like aluminum inproducing asecond phase.

It is therefore possible to employ as little as 3% aluminum by weightwhen using substantial amounts of tin or silicon and obtain the duplexstructure. An illustration of an aluminum bronze alloy containing smallamounts of aluminum and having the duplex metallographic structure is asfollows:

Percentage by weight 3 The presence of alloying elements in a duplex orbeta aluminum bronze structure will not greatly alter the reaction ofthe bronze alloy during heat treatment. However, in some cases, it maytake a longer period of time to produce the necessary metallographicchange in the alloy during heat treatment to produce a satisfactoryincrease or decrease in the accepted modulus of elasticity.

The present invention is directed to a heat treatment to be applied to aduplex or beta phase aluminum bronze alloy to obtain the gammaconstituent in suflicient proportions and distribution to give asubstantial increase in the modulus of elasticity.

For commercial feasibility, the gamma constituent should be present inthe range of about 3 0% to by weight of the alloy. A gamma contentoutside of this range will adversely affect the physical properties ofthe alloy and decrease the usefulness of the alloy for commercial andstructural purposes.

Examples of aluminum bronze alloy compositions in weight percent towhich the heat treatment of the invention can be applied to increase themodulus of elasticity are as follows:

C D E F G balance "fiifi' balance balance balance The heat treatmentconsists of initially heating the alloy to a temperature of over 1050 F.and preferably in the neighborhood of about 1450 F. The alloy ismaintained at this elevated temperature for a period of about one hourand generally for a period of about minutes to 30 minutes per two inchsection of the alloy.

After the heating treatment, the alloy is quenched at a rate of 500 F.to 1000" F. per minute per two inch section to a temperature in therange of about 200 to 400 F. It is necessary that the quench be made atthe above rate for if thequench is slower than 500 F. per minute, toomuch alpha is obtained which will not transform to the gamma constituentduring the subsequent treatment. Conversely, if the rate of quench isfaster than 1000 F. per minute, too much beta is obtained in themetallographic structure which results in too great a proportion of thegamma constituent in the final alloy. This results in the alloy beingextremely brittle. It has been found that a cooling range of about 600F. per minute is satisfactory for most applications.

The cooling may be accomplished by means of oil or water quenching orany other suitable fluid to produce the above mentioned cooling rate.

The resulting structure after cooling when using a duplex phasestructure, is generally alpha face centered cubic crystal with a betamatrix which is a martensitic structure. This phase has a body centeredcubic lattice.

After the alloy has been conditioned properly by the elevatedtemperature treatment and cooled, it is necessary to reheat the alloy inav series of temperature increments to a temperature of about 850 F. to950 F. to obtain the gamma constituent in the desired proportions anddistribution to provide the increased modulus of elasticity.

In the reheating treatment, it is necessary to heat the alloy from thequenched temperature to at least one intermediate temperature below therange of 850 to 950 F. and to hold the alloy at this temperature for asubstantial period of time in order to produce a uniform gamma;,distribution in the alloy. It has been found that low temperatureheating substantially below the 850 to 950 F. range causes nucleazationof the gamma and produces a uniform distribution of gamma throughout thestructure. It has also been found that the greater the number oftemperature increments involved in the reheating, and the accompanyingholding period at these temperatures, the more homogeneous the gammaconstituent becomes.

As an example of the reheating treatment, the alloy, after quenching, isheated to a temperature in the range of 490 F. to 550 F. and held atthat temperature for a period of 45 minutes to 90 minutes per two inchsection of the alloy. After this holding period is completed, thealloyis further heated to a temperature in the range of 675 F. to 725 F.and held at this temperature for a period of 45 minutes to 90 minutesper two inches of section.

After this second increment of heating, the alloy is then further heatedto a temperature in the range of 850 to 950 F. and held at thistemperature for a period of one to two hours per two inches of sectionof the alloy. As previously pointed out, there should be at least oneincrement of heating or soaking before reaching the 850 to 950 F.temperature range and preferably two or more increments of heating andholding at that temperat re.

After the reheating operation, the alloy is furnace cooled to atemperature in the range of 550 to 650 F. and held at this temperaturefor 20 to 45 minutes per two inches of section. The alloy is then cooledto room temperature.

Ordinarily the modulus of elasticity of commercial aluminum bronzealloys is shown at 15,600,000 p. s. i. With the treatment of the presentinvention it is possible 1 to increase the modulus of elasticity above20,000,000

p. s. i. to a value of 24,000,000 p. s. i.

To obtain a substantial increase in the modulus of elasticity and yetretain an appreciable ductility, the alloy should contain the alpha andbeta duplex phase. The beta phase or martensitic structure present afterthe quenching operation acts to bring about an increase ir the modulusof elasticity during the subsequent aging, while the alpha phase servesto give the treated alloy the necessary ductility for structuralpurposes.

If the alpha phase alone is present in the alloy, the modulus ofelasticity will not be altered by the heat treatment. Conversely, ifonly the beta phase is present the modulus may be substantiallyincreased but the elongation isappreciably reduced. Thus, for the mostpurposes the duplex phase is preferred with the proportion of the alphaphase to the beta phase depending upon the elongation desired in thetreated alloy.

With a duplex structure and a properly controlled chemical compositionof alloying elements and the controlled heat treatment of the invention,it is also possible to have attractive other properties when the modulusof elasticity is changed. For example, by employing the presenttreatment with a selective chemical analysis, comprising 10.6% aluminum,3.6% iron, 2.5% nickel and the balance. copper, the modulus ofelasticity can be substantially increased to 24,000,000 p. s. i. and thealloy will have a tensile strength of over 100,000 p. s. i., a yieldstrength of over 60,000 p. s. i., an elongation of a 4% minimum, and aBrinell hardness of approximately 235. Thus, it is possible by employingthe described heat treatment and the proper alloying elements to producea substantially increased modulus of elasticity together withimprovements of other physical properties, when so desired. An alloyexhibiting these properties would be particularly adaptable for use asshafting, bushings or machine members requiring high rigidity.

While the above described heat treatment is directed to maintaining thealloy at given temperature ranges for specified periods per two inchsection of the alloy, it is intended that the time period is to beproportionately increased for sections greater than two inches and proportionately decreased for sections less than two inches.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:

1. A method of increasing the modulus of elasticity of an aluminumbronze alloy having from 3% to 20% aluminum and having a betaconstituent in the metallographic structure, which comprises heating thealloy to a temperature of over 1050 F., cooling the alloy at a rate of500 F. to 1000 F. per minute per two inch section to a temperature below400 F., and reheating the alloy with at least one increment oftemperature to a temperature in the range of 850 F. to 950 F., saidalloy being held at the temperature of the increment and at thetemperature in the range of 850 to 950 F. for a sufiicient period oftime to obtain the gamma constituent in the range of about 30% to byweight of the alloy and thereby produce a substantial increase in themodulus of elasticity.

2. A method of increasing the modulus of elasticity of an aluminumbronze alloy containing from 3% to 20% aluminum and having at least somebeta phase in the metallographic structure, which comprises heating thealloy to a temperature of over 1050 F., quenching the alloy at a rate of500 F. to 1000 F. per minute per two inch section to a temperature inthe range of 200 F. to 400 F., and reheating the alloy from the quenchedtemperature to at least one intermediate temperature below the range of850 F. to 950 F., holding said alloy at said intermediate temperaturefor a period of 45 minutes to 90 minutes per two inch section of thealloy continuing the reheating of the alloy from the intermediatetemperature to a temperature in the range of 850 F. to 950 F., holdingsaid alloy at the temperature in the range of 850 F. to 950 F. for aperiod of one hour to two hours per two inch section ofthe alloy, saidreheating serving to produce the gamma constituent in the alloy in therange of 30% to 70% by weight of the alloy and thereby produce asubstantial increase in the modulus of elasticity of the alloy.

3. A method of increasing the modulus of elasticity of an aluminumbronze alloy containing from 3% to 20% aluminum to produce at least somebeta phase in the metallographic structure, which comprises heating thealloy to a temperature of over 1050 F., cooling the alloy at a rate of500 F. to 1000 F. per minute per two inch section to a temperature below400 F., reheating the alloy to a temperature in the range of 490 F. to550 F. and holding the alloy at said last named temperature range for aperiod of 45 minutes to 90 minutes per two inch section of the alloy,heating the alloy to a temperature in the range of 675 F. to 725 F. andholding the alloy at said last named temperature range for a period of45 minutes to 90 minutes per two inch section of the alloy, and heatingthe alloy to a temperature in the range of 850 F. to 950 F. and holdingthe alloy at said last named temperature range for a period of one totwo hours per two inch section of the alloy, said reheating treatmentproducing the gamma; constituent in the range of about 30% to 70% byweight of the alloy to thereby substantially increase the modulus ofelasticity of the alloy.

4. A method of increasing the modulus of elasticity of an aluminumbronze alloy containing from 3% to 20% aluminum and having at least somebeta phase in the metallographic structure, which comprises heating thealloy to a temperature of over 1050 F., quenching the alloy at a rate of500 F. to 1000 F. per minute per two inch section to a temperature inthe range of 200 F. to 400 F., reheating the alloy from the quenchedtemperature to a temperature in the range of 850 F. to 950 F. in aseries of temperature increments, said alloy being held at eachtemperature increment for a period of minutes to 90 minutes per two inchsection of the alloy and said alloy being held at the temperature in therange of 850 F. to 950 F. for a period of one hour to two hours per twoinch section of the alloy, cooling the alloy to a temperature of 550 F.to 650 F., maintaining the alloy at said last named temperature rangefor a period of 20 minutes to 45'minutes per two inch section of thealloy, and further cooling the alloy to room temperature.

5. An aluminum bronze alloy containing from 3% to 20% by weight ofaluminum and having a modulus of elasticity in the range of 21,000,000p. s. i. to 24,000,000 p. s. i. and being characterized by having from30% to by weight of the gamma constituent in the metallographicstructure, said alloy being produced by heating the alloy to atemperature of over 1050 F., quenching the alloy at a rate of 500 F. to1000 F. per minute per two inch section to a temperature in the range of200 F. to 400 F., and reheating the alloy from the quenched temperatureto a temperature in the range of 850 F. to 950 F. in a series oftemperature increments, said alloy being held at each temperatureincrement for a period of 45 minutes to minutes per two inch section ofthe alloy and said alloy being held at the temperature in the range of850 F. to 950 F. for a period of one hour to two hours per two inchsection of the alloy, said reheating serving to produce the gammaconstituent in the alloy in the range of 30% to 70% by weight of thealloy and thereby increase the modulus of elasticity to theaforementioned range.

References Cited in the file of this patent Aluminium Bronze, issued bythe Copper Development Assoc. (London), N0. 31 (1939), pages 31-60.

Metal Progress, vol. 38, July-Dec. 1940, pages 791, 793, 794, 797.

1. A METHOD OF INCREASING THE MODULUS OF ELASTICITY OF AN ALUMINUM BRONZE ALLOY HAVIG FROM 3% TO 20% ALUMINUM AND HAVING A BETA CONSTITUENT IN THE METALLOGRAPHIC STRUCTURE, WHICH COMPRISES HEATING THE ALLOY TO A TEMPERATURE OF OVER 1050*F., COOLING THE ALLOY AT A RATE OF 500*F. TO 1000*F. PER MINUTE PER TWO INCH SECTION TO A TEMPERATURE BELOW 400*F., AND REHEATING THE ALLOY WITH AT LEAST ONE INCREMENT OF TEMPERATURE TO A TEMPERATURE IN THE RANGE OF 850*F. TO 950*F., SAID ALLOY BEING HELD AT THE TEMPERATURE OF THE INCREMENT AND AT THE TEMPERATURE IN THE RANGE OF 850 TO 950*F. FOR A SUFFICIENT PERIOD OF TIME TO OBTAIN THE GAMMA2 CONSTITUENT IN THE RANGE OF ABOUT 30% TO 70% BY WEIGHT OF THE ALLOY AND THEREBY PRODUCE A SUBSTANTIAL INCREASE IN THE MODULUS OF ELASTICITY. 